Press brake tables or the like often have machining defects which must be corrected by controlled deformation. It is also known that the very high forces to which these tables are subjected during a sheet-metal bending operation or the like cause additional deformation whose maximum amplitude obviously occures at the center of the table, i.e. in the area furthest from the columns that support it, and depends on the characteristics of the bending performed as well as the nature and thickness of the sheet to be bent.
To allow their users to correct this type of deformation, these tables are often equipped with means permitting them to be deformed in the opposite direction while conferring on them a degree of convexity whose magnitude depends on the characteristics of the bending to be performed and the nature of the sheet to be bent as well as on any machining defects.
Known tables with adjustable convexity with which certain press brakes are equipped are generally composed of two superimposed horizontal plates, braced by two superimposed rows of blocks forming wedges associated pair-wise. The blocks in the bottom row are linked to the upper face of the lower plate which in turn is connected to the fixed base of the machine. Those in the upper row are linked to the lower face of the upper plate. The faces in contact of each pair of blocks form with the horizontal a specific non-zero angle. Mechanical, electrical, pneumatic, hydraulic, or other means are provided to allow the movable upper plate to be shifted from one extreme starting position in a direction in which, by sliding on the lower blocks, the upper blocks and consequently the upper plate are displaced upward.
The convexity of this table in therefore adjusted simply by shifting the movable upper plate relative to the fixed lower plate so that the blocks in the upper row slide on those in the lower row, with the slopes of the faces of the blocks in contact having the effect of conferring a certain convexity on the upper face of the upper plate.
In these known tables, the slope angle of the faces in contact of each pair of blocks is constant and invariable, and the deformation which can be conferred on the upper plate is therefore linear and fixed since it is determined by the aforesaid slopes. Consequently, the shape of this deformation can be changed only by replacing one or more pairs of blocks by blocks with different slopes, which obviously necessitates complete disassembly and reassembly of the table.